This invention relates generally to thermal management of battery packs, and more particularly to the use of microencapsulated phase change materials in conjunction with a liquid heat exchange medium to regulate the temperature of automotive battery packs.
Lithium-ion batteries are being used in automotive applications as a way to supplement, in the case of hybrid electric vehicles (HEVs), or supplant, in the case of plug-in electric vehicles (PEVs), conventional internal combustion engines (ICEs). In either variant, HEVs or PEVs belong to a larger class of vehicles known as electric vehicles (EVs). The high volumetric heat generation rate and generally passive construction of lithium-ion batteries provides both the durability and functionality needed to serve as a propulsion system for cars, trucks, buses, motorcycles and related automotive or vehicular platforms.
Temperature is one of the most significant factors impacting both the performance and life of a battery. Extremes (such as those encountered during protracted periods of inactivity in cold or hot environments, or due to extended periods of operation and concomitant heat generation on hot days) can negatively impact the ability of the battery to operate correctly, and in severe cases can destroy the battery entirely. In one particular scenario, starting operation of a vehicle parked on a hot day could expose the battery to a temperature rise in excess of its safe limits absent some device that is immediately available to remove the excess heat generated by such operation. Side effects of prolonged exposure to high temperatures such as this may include premature aging and accelerated capacity fade, both of which are undesirable. Conventional heat dissipation methods such as forced air and liquid cooling may prove to be effective at avoiding such side effects, but they add to overall vehicular system weight, complexity and parasitic power requirements.